Supplies the CSS bodies of the track's WebVTT STYLE blocks (which carry
::cue rules), so the renderer can style cue classes. Optional — a
renderer may ignore authored styles.
Renders the active cues of track, listening for cue changes. Passing
null clears anything rendered and detaches from the previous track.
A TextTrackRenderer that paints cues as HTML into element. Mount
elementover the video; it stacks cues at the bottom, centered, and positions any cue that carries explicit WebVTT settings. The DOM track is expected to be'hidden'so only this renderer paints.